Apparatus for determining relative times of development of photographic plates or films for different temperatures.



APPARATUS FOR DETERMINING RELATI A. WATKINS. VE TIMES OF DEVELOPMENT OF PHOTOGEAPHIO PLATES 0R FILMS FOR DIFFERENT TEMPERATURES. APPLIUATIOII FILED JULYZ. 1908.

Patented Sept. 7, 1909.

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as 66 e4- 62 WRTNESSES \XAXL a a INVENTOR A. WATKINS. APPARATUS EOE DETERMINING RELATIVE TIMES OF DEVELOPMENT OF PHOTOGRAPHIG PLATES 0R FILMS FOR DIFFERENT TEMPERATURES.

APPLICATION TILED JULY 2. 1908.

I Patented Sept. 7, 1909.

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WITNESSES TQM/Thou 31M 11 j county of Hereford, England, photographic- PTENT @FFltQE.

ALFRED WATKINS, OE HEREEOED, ENGLAND.

APPARATUS FOR DETERMINING RELATIVE DEVELOPMENT OF PHOTO- GRAPHIC PLATES 0R FILMS EOE DIFFERENT TEMPERATURES.

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Specification of Letters Patent,

Patented Sept. a, race.

n a filed July 2, 3908. Serial No. 441,657.

-T0 all. whom it mag concern: t I

Be it known that I, ALFRED WATKINS, a subject of the King of- Great. Britain, residing at The Imperial Mills, Hereford, in the apparatus manufacturer, have invented certain new and useful Improvements in an Apparatus for Determining the Relative Times of Development of Photographic Plates or Films for Different Temperatures,

of which the following is a specification.

It is well known that the rate or speed of development of photographic films or plates varies with the temperature in a manner which is very approximately represented for ordinary ranges of temperature'by the equation +t)= Z where V denotes the speed of development at T C. (T-I-t) denotes the speed of de- .1 velopment at (Ta-t) C. and 7c denotes the temperature coetlicient for 1 C. If, therefore, the speed of development of a given plate is determined experimentally for a given developer at two different temperatures, thetemperature coetlicientfor that developer and plate can'be calculated, and the value obtained used to determine the speedof development or relative time of development for. other temperatures.

The present invention has for its object to provide an apparatus, by means of which the relative time of development for any temperature can be quickly ascertained when the correct time of development for a given temperature is known. The apparatus com prises two relatively movable scales, one of which is a logarithmic scale representing times or duration of development, andthe other an equal division degree scale the length or value of the divisions of which is determined by the value of the temperature coetficient proper to the plate and developer used. By setting the scales with the division corresponding to the known time of devclopment at a given temperature in register with the division representing that temperature, the relative time of development for any other temperature can be immediately read off.

For developers which are sent out in liquid form one scale may conveniently be pasted around the bottle and the other displayed on a band encircling the bottle and ;rotat able thereon. The value of the temperature scale divisions would be that proper ito the temperature coefiicient for the developer contained in the bottle.

For developers which are sent out in other ikinds of packages the movable scale might ';be displayed around the edge of a'circular Q'disk rotatable concentrically with the fixed fscale; or a translationally movable scale m1ght be provided as for example if the of the slot.

eter itself may be used as the temperature scale with respect to which the logarithmic scale set.

When a thermometer is supplied as partof the apparatus the scale of the therm'ompackage is of ordinary match-box form one The invention isillustrated as applied to ,a calculator adapted to be used for different temperature coetlicients, Figure 1 showing a translationally adjustable form of the apparatus and Figs. 9,3 and 4 a rotary form, Figs. 2 and 3 being respectively front and rear views and Fig. 4 a section on line 44 The temperature scale consists of a series of lines B equally disposed and radiating from a; point, and the logarithmic scale A constituted bya series'of'divisi'onal lines is arranged to be-adjustable longitudinally as well as transversely to these lines so that it can be read with respect to temperature scales havingditfer'ent constants. To facilitate setting the logarithmic scale to the proper distance along the radiating lines, an auxiliary scale C of temperature coeflieient values may be provided with respect to which one or other of the scales of the calculator is first set. When the logarithmic scale A is on a straight'bar a (Fig. l), translationally movable longitudinally in a frame Z) which itself is adjustably mounted on the plate 0 carryingthe temperature scale so that the bar a. can be-moved in the frame across the plate a and with the frame along the plate 0, the radiating lines B of the temperature scale would be straight, but when the logarithmic scale A is dlsplaced on a rotatable disk at (Figs. 2 and 4:) movable along the radiating temperature lines, these lines 13 are curved outwardly from a straight standard temperature line 13. In both casesthe scale of temperature represented by the intersection of the edge of the bar a or disk a with the radiating temperature lines B must be an equal division scale, or only depart therefrom in accordance with divergence of the law connecting speed of development and temperature from that given at the beginning of the present specification.

In the rotary apparatus the disk a is mounted on a slide 6 which is adjustable translationally on the plate 0' carrying the temperature scale in such manner that the center of the disk moves along the straight or standard line 13 of the temperature scale. In this case the scale C of temperature coefficients is more conveniently engraved or otherwise displayed on. the rear face of the slide 1) and set with respect to a fiducial mark on the rear face of the plate 0 as shown in Fig. 3, or alternatively the scale C may be on the plate and the fiducial mark on the slide, as shown respectively in broken lines at b and b a As shown in the drawings the temperature scale B is in Fahrenheit degrees and the temperature coefficient numerics are those proper to 10 F.

- Having thus described the nature of my said invention and the best means I know of carrying the same into practical effect, I claim 1. An apparatus for determining the relative times of development of photographic plates or films for different temperatures by the cooperation of two relatively movable scales, consisting of a scale member having thereon a series of lines constituting an equal division scale representing degrees of temperature, a second scale member bearing a single scale comprising a series of divisional lines constituting a logarithmic scale representing times of development, which divisional lines cooperate with the lines on the first scale member to indicate the times of development, and means for adjusting one scale member with respect to the other; substantially as described.

2. An apparatus for determining the relative times of development of photographic plates or films for different temperatures by the cooperation of two relatively movable scales, consisting of a scalemember having thereon a series of radiating lines constituting an equal division scale representing degrees of temperature, a second scale member bearing a single scale comprising a series of divisional lines constituting a logarithmic scale representing times of development,

which divisional lines cooperate with said radiating lines to indicate the times of development, and means for adjusting one scale member withfrespect to the other; substantially as described.

3. In apparatus for determining the relative times of development of photographic plates or films for different temperatures by the cooperation of two relatively movable scales consisting of a scale member having thereon a series of radiating lines constituting an equal division scale representing degrees of temperature and a second series of lines constituting a second scale representing temperature co-efficients, a second scale member bearing a single scale comprising a series of division-a1 lines constituting a. logarithmic scale representing times of development which divisional lines are adapted to cooperate with said radiating lines to indicate the times of development, means for adjusting the second scale member with respect to the said second scale of the first scale member and means for adjusting the second scale member also with respect to the said equal division scale on the said first scale member; substantially as described. v

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

ALFRED WATKINS.

lVitnesses CHARLES BRINDLEY BEDnoE, OWEN LEVI BRADLEY. 

